This invention in general relates to optical communications and in particular to integrated optic grating multiplexers.
Wavelength division multiplexing (WDM), the simultaneous transmission of several signals on a single path, is a technology that is fundamentally important in fiber based communications sytems because of its impact on system configuration, performance, and cost. One major advantage of this technology is its ability to increase system capacity by increasing the number of channels that can be carried per fiber. With increased capacity, fiber requirements and associated fiber costs decrease, and already installed systems can more easily be upgraded to handle subsequent increases in traffic. Also, different modulation schemes can be used on assignable channels to enhance flexibility and overall system design.
Wavelength selective multi-demultiplexers may be classified as active, such as multiwavelength sources or detectors, or passive, such as dielectric filters and angularly dispersive devices like prisms or gratings. Various forms of passive gratings are known. Among them are included line gratings and Fresnel gratings. These kinds of gratings have been proposed and also demonstrated as evidenced by the literature. All high resolution gratings require submicron lithography, or equivalent precision fabrication, since the line periodicity required for adequate resolution is of the order of a wavelength. Consequently, it is relatively difficult to exploit conventional photolithographic integrated optics fabrication technology to manufacture line gratings to the precision required for WDM applications.
However, another type of grating, the echelon grating, is well known in bulk optics and can achieve the high resolution needed for WDM purposed which supplies high relative precision without the need for the high periodicity of the line gratings. Because of the importance of wavelength division multiplexing technology, and the difficulty of easily fabricating angularly dispersive devices, it is a primary object of the present invention to provide an integrated optic echelon grating that can be easily fabricated.
It is another object of the present invention to provide an integrated optic echelon grating that can be fabricated utilizing conventional photolithographic and etching techniques.
Other objects of the invention will in part be obvious and in part appear hereinafter when read in connection with the detailed description to follow.